The present invention relates to an automatic mounter for mounting electronic circuit parts on a circuit board, or more in particular to an automatic electronic-part mounter equipped with the function to correct the position of a part-mounting section of the circuit board.
In preparing a circuit board, a part is inserted in a board formed with a circuit pattern and holes for inserting terminals of the part, and they are soldered. Among these processes, an automatic electronic-part mounter explained below has been used to insert the part. Such an automatic electronic-part mounter comprises a movable table for placing a board thereon, a hand unit for holding an electronic part, and a part supply unit for supplying an electronic part.
The movable handle is movable as desired along the X and Y coordinate system, and carries a circuit board thereon to place the same in position.
The hand unit includes four hands movable between the supply unit and a predetermined position on the movable table to transport a predetermined electronic part from the part supply unit to a part-mounting section on the circuit board placed on the surface of the movable table and to mount the part on the part-mounting section.
Since there is an error both in the position of each part-mounting section of the circuit board and in the position of the circuit board on the movable table, an attempt to mount an electronic part directly at the part-mounting section may not succeed.
In a conventional method of correcting such a problem, the actual position of each part-mounting section is confirmed by sensor and the positional data is corrected before moving the movable table in order to mount an electronic part accurately in position despite "of" any displacement. In the case where holes for inserting leads of an electronic part are formed in the part-mounting section of the circuit board, the position of the part-mounting section may be confirmed by such insertion holes. A sensor suitable for such a purpose is of optical type including a projector for projecting light toward the circuit board and a photo-detector for receiving the light passed through a predetermined insertion hole of the circuit board. In the positioning process, the movable table is moved if the center of an insertion hole fails to coincide with the optical axis of the sensor, and when they come to coincide with each other, the prevailing position of the movable table is stored in a buffer memory of a control unit. In the subsequent processes of inserting a lead into this insertion hole, the stored positional data is used to move the movable table, thereby positioning the movable table accurately.
The operation of such a conventional automatic electronic-part mounter is shown in the flowchart of FIG. 1. First, as shown in step 1-1 the movable table is moved to determine the provisional position of an insertion hole against the sensor. At the next step 1-2, the displacement of the insertion hole is detected, followed by step 1-3 where the position of the insertion hole against the hand that has grabbed an electronic part in advance is determined by use of the result of detection of the displacement. Then the lead of the electronic part is inserted into the insertion hole. This operation is repeated for each insertion hole.
FIG. 2 shows relative positions of the circuit board, the sensor and the hand in the above-mentioned case. In FIG. 2, reference character B designates the circuit board, character O an origin assumed to exist on the circuit board by way of explanation, characters h.sub.1 to h.sub.3 insertion holes, H.sub.1 to H.sub.4 four hands used for insertion, S the sensor, v.sub.1 to v.sub.3 vectors representing the positional relations between each of the insertion holes h.sub.1 to h.sub.3 and the origin O, character v.sub.O a vector representing the positional relations between the insertion hole h.sub.1 and the sensor S, and m.sub.1 to m.sub.4 vectors representing the positional relations between the sensor S and each of the hands H.sub.1 to H.sub.4. By using these relative positions of FIG. 2, the movement of the circuit board B mounted with electronic parts in the sequence shown in FIG. 1 is illustrated by solid lines in FIG. 3 as a trace or the origin O. In FIG. 3, points p.sub.1, p.sub.3, p.sub. 5 designate the positions of the origin O with the insertion holes h.sub.1, h.sub.2, h.sub.3 positioned to the sensor S respectively, and points p.sub.2, p.sub.4, p.sub.6 the positions of the origin O with the insertion holes h.sub.1, h.sub.2, h.sub.3 positioned to hands H.sub.1, H.sub.2, H.sub.3, respectively. The explanation about the hand H.sub.4 will be omitted.
In this conventional system, the disadvantage is a comparatively long time required for repeating the movement of the origin O of the circuit board B from the initial position p.sub.1 to p.sub.2 to p.sub.3 to p.sub.4 to p.sub.5 to p.sub.6 in the process of insertion of parts.